1. Field of the Invention
The present invention relates to a lighting apparatus with LEDs (light emitting diodes).
2. Description of the Related Art
The research of light emitting device has been widely carried out and developed so far by utilizing an LED chip and a phosphor (fluorescent pigment, fluorescent dye, or the like) acting as wavelength conversion material which is excited by a light from the LED chip to emit a light of a color different from a luminescent color of the LED chip. The light emitting device enables to emit a light of a color different from the luminescent color of the LED chip by combining the LED chip with the phosphor, leading to commercialization of a white light emitting device (generally referred to as white LED) and the like. The white light emitting device emits a white light (light emission spectrum of white light) by a combination of the phosphor with the LED chip emitting a blue color light, an ultraviolet light, or the like.
As the output of the LED chip is increased recently, the white LED has been actively studied and developed for utilized as a lighting apparatus. Japanese Patent Publication No. 2003-59332 proposes an LED unit (an LED module) comprising a circuit board mounting a plurality of white LEDs.
Japanese Patent Publications No. 2003-168829 and 2001-203396 propose structures configured to efficiently exhaust a heat, accompanied with the high light output, which is generated from each of the light emitting parts of LED chips. In the conventional LED units, however, the respective LED chips are electrically connected with conductive patterns on a circuit board directly, so that the heat generated from the LED chips spreads over the circuit board through electrical connection parts. Thus, a metal-made heat radiative board is necessarily attached to the bottom surface of the circuit board for enhancing thermally conductive performance over a whole range of the circuit board, thereby increasing a cost of the circuit board. Furthermore, when comprising such LED unit, the lighting apparatus requires a dielectric sheet to be interposed between a metal-made main body and a metal plate of the circuit board so as to protect the LED unit from a lightning surge as well as enhancing thermally conductive performance by thermally coupling the metal plate of the circuit board to the metal-made main body including one part of the lighting apparatus. In this case, however, the thermally conductive performance cannot be sufficiently made due to two dielectric layers, dielectric layer of the circuit board and the dielectric sheet, interposed on thermally conductive path from the LED chip to the metal-made main body through the circuit board.